A turbine is a well-known energy conversion apparatus, which is characterized by a rotating member that turns in response to an applied force. Typically, this force is generated by directing a high pressure working fluid such as superheated steam at the rotating member such as a series of blade rows which extend radially from a rotor. The efficiency of the turbine depends upon its ability to maximize the conversion of the working fluid energy into rotation of the rotating member. Sealing devices are therefore employed about the rotating member to contain the working fluid to working spaces within the turbine.
Sealing devices used in turbines are known variously as steam seals, gland seals, labyrinth seals, steam packings, diaphragm packings, and pressure packings. A fundamental component of these seals is a sealing strip. The sealing strip is a ring shaped structure which is typically provided as several arcuate sealing segments. The sealing strip encircles the rotating member and occupies radial space between the rotating member and the turbine casing or other surrounding structure.
FIG. 1 illustrates a seal system 10 having a plurality of simple circumferentially-extending sealing strips 12 arranged radially from a stationary member such as a turbine casing 11, and a series of simple circumferentially-extending sealing strips 14 arranged radially from a stationary member such as a diaphragm 13 to form a small radial clearance between inner surfaces of the sealing strips and a circular surface such as a blade cover band 15 or a rotor 18, respectively, to limit the amount of gas that passes therebetween.
FIG. 2 illustrates a “Vortex Shedder Seal” segment 20, a plurality of which are employed as a sealing strip for reducing the gas pressure ahead of a seal system, and also reduce the pressure differential across the seal system. See. U.S. Pat. No. 5,735,667 issued to Sanders et al. As shown in FIG. 2, “Vortex Shedder Seal” segment 20 includes a plurality of spaced apart teeth having a plurality of outwardly-extending portions 28 adjacent to openings between the teeth which extend into a high pressure region to generate turbulence in a tangential fluid flowing as indicated by a curved line R adjacent to the seal strip for producing and shedding vortices in the high pressure fluid to generate reduced pressure adjacent to the seal in the high pressure region. As shown in FIG. 3, another “Vortex Shedder Seal” segment 30 has a plurality of outwardly-extending dimples 38 that extend into a high pressure region to generate turbulence in the high pressure tangential fluid flowing as indicated by a curved line R adjacent to the seal for producing and shedding vortices in the high pressure fluid to generate reduced pressure adjacent to the seal in the high pressure region. For example, the producing and shedding of vortices increases kinetic energy of the working fluid which reduces the pressure of the working fluid in front of the vortex shedder seal.
Additional background information may be found in Sanders, Turbine Steam Path Engineering for Operations & Maintenance Staff, 1988, the entire contents of which are incorporated herein by reference.